The present invention relates to a closed cycle refrigeration system utilizing a remote condenser and constructed so as to improve the efficiency of operation of the system and reduce the power consumption.
This invention is related to the subject matter disclosed and claimed in U.S. Pat. application Ser. No. 57,350 filed July 13, 1979 by Fayez Abraham and Edward Bowman, and assigned to Tyler Refrigeration Corporation; the disclosure of said Ser. No. 57,350 is incorporated herein in its entirety by reference.
In the basic closed cycle refrigeration system, gaseous refrigerant is compressed to a high temperature. The high temperature compressed gas passes through a condenser where it gives up heat to the ambient and is condensed to a liquid. The pressure within the condenser is maintained at an appropriate level so that the gaseous refrigerant will be transformed into a liquid at a temperature level higher than the ambient air. The condensed liquid refrigerant is collected in a receiver and is conducted from a the receiver to an expansion valve, or other metering device, where it is expanded and passed through an evaporator within a display case. As the expanded liquid refrigerant flows through the evaporator, it extracts heat from the display case and is converted back to a gaseous state. This gaseous refrigerant is returned to the compressor and the cycle is continued.
Throughout the present description, references to "high side" are to the high pressure side of the system (upstream of the expansion valve or other metering device) or portion thereof. References to "low side" are to the low pressure side of the system (downstream of the metering device) or portion thereof. The liquid side of the system is generally considered to be between the outlet of the condenser and the metering device. The low pressure gas side or "suction side" lies between the metering device and the compressor. The metering device referred to herein is that device that controls the flow of liquid refrigerant to the evaporators.
In order to condense hot gaseous refrigerant, the condenser must be able to give up refrigerant heat to the ambient. Therefore, the condenser must operate at a higher temperature than the ambient. Traditionally, the condenser is operated at a preselected design temperature level, determined as a function of the highest ambient temperature during a normal period of the warmest season in a particular area. The condenser is then operated to condense the gaseous refrigerant at a temperature at least 10.degree. F. above the design temperature. Thus if the design temperature is 90.degree. F., then the condenser design temperature is normally set at 100.degree.l F.
With the advent of the energy crises, and steadily rising utility costs, significant attention has been given to improving the energy efficiency of refrigeration systems. In large installations, such as supermarkets, there are typically large numbers of refrigerated display cases and hence, typically a plurality of compressor units are employed to satisfy the heavy refrigeration load required under certain conditions, such as during the warmer periods of the year. It is highly desirable to increase the operating efficiency of the refrigeration system and thereby reduce its operating cost. Such savings can be substantial for large installations.
Increased operating efficiency of the overall system can be achieved, at least in part, by improving the operating efficiency of the compressor unit (the compressor unit may comprise one or more individual compressors connected in tandem, i.e. parallel, or in series). One way to improve compressor unit efficiency is to increase the compressor capacity. By improving the capacities of the compressors of a tandem coupled compressor unit, there are times when less than all of the compressors need to be operated in order to run the refrigeration system. This results in a savings in the power consumption of the refrigeration system.
It has been recognized that the design temperature is only likely to occur a few days in a year, and then only during the day and not at night. In light of this, refrigeration systems have been modified so that the condenser operating temperature follows the ambient temperature while always remaining at least 10.degree. F. above the ambient temperature.
By decreasing the condensing temperature 10.degree. F., the compressor capacity will increase 6%. Consequently, if the condensing temperature is dropped from 100.degree. F. to 75.degree. F., for example, the compressor unit capacity will increase by approximately 15%; simultaneously, the compressor unit power consumption will be reduced. The effect of the increase in compressor unit capacity will result in an approximately 8% reduction in power consumption for every 10.degree. F. drop in condensing temperature, assuming a constant refrigeration load. Consequently, the drop in the condensing temperature from 100.degree. F. to 75.degree. F. will reduce the power consumption of the refrigeration system by about 20%, assuming a constant refrigeration load.
The efficiency of the compressor unit also can be improved by subcooling the liquid refrigerant since the refrigerant will then extract 15% to 25% more heat per pound circulated. For every 10.degree. F. subcooling of the liquid refrigerant, the compressor efficiency will increase by 5%. This improvement in the efficiency of the compressor also results in a reduction in the power consumption.